Changed visibility test
Changed visibility test

I don't know if these are new features, or if the writer of visibility.js didn't know about them, but they seem to work.  One test looks for the element's offsetParent.  The other uses window.getComputedStyle.  In my tests, I need both.  Getting visibility right makes SitePassword work on 80+% of tested sites, up from 60+%.

alanhkarp/SitePassword,alanhkarp/SitePassword